The present invention relates to the measurement of signal parameters, and more particularly to a method for displaying timing pulse jitter, such as horizontal sync pulse jitter for a video tape recorder (VTR) when the VTR changes heads at the end of a field of video data.
Commercial VTRs play back recorded video data via record/playback heads for display on a television monitor. At the end of each video field the VTR changes heads which induces a large amount of horizontal sync pulse jitter for a few lines at the end of the video field. Other sources of horizontal sync pulse jitter in a VTR are the varying tape tension and the mechanical capstans. At present there are no instruments capable of measuring the amount of this head change induced horizontal sync pulse jitter. There are presently two techniques for measuring VTR jitter. The first technique, as exemplified by the Shibasoku 875C VTR Jitter Meter, uses a delay line having a delay equal to one horizontal video line to obtain an incremental value between lines which can be displayed on an oscilloscope. The display is gated off during the vertical interval since the technique cannot handle the vertical pulses or large variations caused by the head changes at the end of each field. The other technique, as exemplified by the Meguro MK-611A and MK-612A Jitter Meters, uses an analog genlock system which also cannot handle rapid or large changes.
What is desired is a timing jitter measurement method which can accurately reflect rapid and large timing pulse jitter changes, such as those changes in horizontal sync pulse jitter due to VTR head switching.